Commercial swivels are used to connect lifting or pulling lines to loads. The swivel permits relative rotation between the line and the load. Arrangements of angular contact ball bearings are commonly used in the higher performance end of commercially available swivels. The arrangement normally used supports a load in only the hanging weight direction and does not provide for load bearing characteristics in the opposite axial direction or for radially applied loading. For example, U.S. Pat. No. 2,466,243 to Johnson discloses a swivel used as a component in a fishing lure. The swivel utilizes ball bearings to provide a rolling contact between two spindles and their respective annular bearing surfaces. The swivel relies on the bearings during times when the spindles are being pulled apart. The bearings would serve no useful function when the swivel is subject to compressive or radial forces. The sealing quality of the swivel relies on the fit between the spindles and the body of the device. Another reference, U.S. Pat. No. 2,811,378 to Kalista, discloses a heavy tension load safety swivel. This swivel is not intended nor suitable for use in conditions involving compression loads or radial loads. A sealing ring is provided to protect the bearing elements from contaminants. U.S. Pat. No. 4,687,365 to Promersberger discloses a load limited swivel connector. This device is adapted for use with only tension loads, and in fact incorporates a safeguard to protect the load lines connected on either side of the swivel.
In such swivels, a rotational force is commonly applied through the torque developed from reeling in spirally wound fiber or wire rope which would cause the load to rotate if not counteracted. The torque is normally decoupled in crane operations and other lifting applications by interposing a swivel designed to operate passively under solely tension loading conditions between the lifting cable and the swivel. As previously stated, the higher performance end designs of such swivels usually utilize angular contact ball bearings which are designed to provide maximum support in one direction and are oriented within the swivel so as to provide support in one axial direction only. Users of commercially available swivels marketed for use in these and other smooth lift applications are generally cautioned against the use of the swivels under side loading or backloading conditions and against the use of such swivels in liquid or liquid-solid slurry environments. At least one previous design has attempted to use ball bearings to provide multidimensional support for a swivel. U.S. Pat. No. 2,651,533 to Miller discloses a swivel for a loading hook. A series of vertically stacked annular ball bearing sets are fitted within the bore of the swivel. This reference states that the bearings distribute radial, axial tension, and axial compression loads. The bearings, however, are of standard design, and are not adapted for loads in any particular direction. Although they can probably distribute light multidirectional loads adequately, the bearings probably cannot handle a large load in any one direction due to the fact that each bearing must be able to withstand a load in any direction. Such a shortcoming limits the uses to which the swivel may be put. A sealing ring is used to keep the bearings free from contamination.
The one-directional thrust orientation of most angular contact bearings provides the stability required for effective sealing only when the unit is subjected to the thrust load in one direction. Thus, when loaded or subject to force in the intended direction of use, an angular contact bearing exhibits superior support characteristics, but when the unit is not loaded or is reverse loaded it has no stability and allows relative radial movement between the inner and outer elements in the seal area. This movement renders the seal ineffective, allowing possibly damaging material to enter the bearing housing area, and allowing lubricants or other essential materials to exit the bearing housing area.
Swivels utilized in underground boring and certain deep sea applications, however, experience bi-directional axial loading as well as side thrust components of loading and require multidirectional support. In these and other applications, swivel mechanisms are also exposed to sandy, liquid, or liquid-particulate solids type environments. The body of the swivel, which contains the bearings, must therefore be sealed against penetration by elements of such an environment regardless of the direction of loading or thrust at any given time. Other swivel devices have been used for such applications. U.S. Pat. No. 4,911,579 to Lutz et al. discloses a swivel arrangement for connecting a boring or reaming tool to a cable. As the boring or reaming tool creates a conduit for a cable, the cable itself is pulled along behind the tool and installed in the same step. The tool is divided into two main parts which are connected by a swivel mechanism. The swivel mechanism ensures that the cable does not twist or rotate with the motion of the boring tool. The design of the swivel mechanism itself is not described in detail. Rather, the reference is directed primarily to the method of connecting the swivel mechanism to the two main parts of the device.
In deep sea applications, this task is more complicated in that the seal must also be able to sustain high water pressure. The requirements of high reliability under bi-directional axial loading and side thrust loading and operation in a hostile medium have not been provided by existing swivel designs.